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Tuesday, Symposium: Cortical Sources . . . 37 Symposium 4 Tuesday, Symposium: Cortical sources . 37 MET,BOLICPVMP~NG IN INSECT LKSCIE ,WD RESTING MEMBRXW ELECTROGENESIS Comparison of electrical activity and ionic currents in an isolated M.J. KATKOWSKA & B. GRAPEL. N. Copernicus Univ., Inst. of Biology and axon and in an isolated neuron. Environmental Protection. Dept. of Animal Physiology, To&. Poland Stankiewicz M.', Grolleau F.~,Lapied B.~,Kadziela w.', Pelhate M.~ A studj of the literature concerning the resting potential (RP) of insect muscle Inst, of Biology and Environment Protection. N.Copernicus Univ , Torun. Poland reveals a number of apparent departures from the situation found in other (I),Lab.of Neurophysiology. EREA CNRS 120. Angers, France (2). excitable cells. The Insects. adult Colorado beetle and mealworm, and mealworm The comparative approach to investigation of the axonal and larva. chosen to this study differ much in their haemolymph ionic content (e.g neuronal mechanisms underlying rythmogenesis in invertebrates has lead Colorado beetle's haemolymph contains only 2 mmol.l-' of NaC) and so they have to an important conclusion that rythm generation is the result of complex ditferent ion~c requirements for the resting membrane potential (RMP) interactions between cellular, synaptic and network properties. The aim of maintenance and the contnbution of pumps to it. The present study examines the this study is to compare the membrane properties of insect giant axon, tlme dependence of the RP In muscles of studied insects and tries to determine the which propagates action potentials and insect neurosecretory cells called role of metabolic pumping in the genesis of tlus potentla1 using of sodium pump dorsal unpaired median (DUM) neurons involved in the modulation of idubitor - ouabain and in the case of Colorado beetle, K-H pump inhibitor - SCH skeletal and/or visceral muscles via the release of octopamine. Giant axon 28080. Eqxriments were performed in situ on Indirect flight muscles of adult and DUM neuron are endowed with a specific set of ion currents that shape Colorado beetle and mealworm, and on ventral longitudinal muscles of mealworm and define their integrative properties. For a detailed study of the larva by "soaking" the muscles in standard (respective for each of Insects studied) biophysical and pharmacological properties of these currents, application or modified salines for 2h. and impaling several cells in each preparation. The of double oil-gap method and patch-clamp technique to giant axon and conventional microelectrode technique was used. The control mean values of DUM neuron respectively, has proven a useful strategy. The axonal muscle RP in adult Colorado beetle and mealworm and mealworm larva, membrane properties can be described by a capacitance in parallel with measured just after the equil~brationtime, were, respectively. 75.0, 50.6 and 38.3 three types of currents: a fast transient sodium current sensitive to mV. and only slightly decreased with time. In Colorado beetle's muscles. tetrodotoxin, a delayed rectifier (DR) potassium current blocked by 4- application of I mmol.1-' ouabain caused a membrane hyperpolarizationof around aminopyridine and a leak current. They allow to generate only short 6 mV after 90 and 120 min. Application of 1 mmol.l-' SCH 28080 resulted in a evoked action potentials (0.5 ms in duration) however at high frequency slight decrease of the RPvalue. In the muscles of adult mealworm. ouabain caused (up to 300Hz). By contrast DUM neurons spontaneously generate electrical a slight. gradual hyperpolarizatlon of the RP (by 2.8 and 4.5 mV after 1 and 2h, activity in the abscence of synaptic input or other external stimuli. DUM respectively). Essentially identical results have been obta~nedon ventral muscles neurons can fire repetitive impulses with remarkably regular intewals. The of mealworm larva. Thus. it seems that the skeletal muscles of studied insects do study of ionic mechanisms underlying this spontaneous electrical activity not contaln an ouabain-sensmve metabol~cmechanism, the functioning of which reveals that DUM neuron soma possess voltage-dependent Na channels is necessary for long-term maintenance of the RMP. In insects, like Colorado responsible for the depolarizing phase and background Na channels beetle, with unconventional ion levels in their haemolymphs, at least the NaC playing a role in driving the membrane potential to threshold of action gradient may be in the reverse direction, and the outward K- gradient much potential. In addition DUM neurons also display multiple K+ currents such reduced. The operation of the classical NaA-K+pump would not be suitable for as IKN,, IKca, IKDR and IKA like, involved in the repolarization, these conditions, and, therefore, such pumping mechanism may not be present in afterhyperpolarization and regulation of the firing frequency. Moreover two these msects. If an electrogenic pump is present in muscle fibers of studled distinct types of low voltage activated ca2+ currents: a transient and a insects, lts properties dlffer appreciably from those described for the electrogenic maintained current have been described. The first one is involved in the sodium pump which appears in many nerves and muscle cells. initial part of the predepolarization and the second one participates in the last two-third of this predepolarization. Symposium 4 - Cortical sources of oscillation DOES IN VITRO THETA-LIKE ACTIVITY REFLECT Oscillatory brain dynamics in auditory and visual PHYSIOLOGICAL AND PHARMACOLOGICAL PROPERTIES system OF EPILEPTIFORM DISCHARGES ? Jan Konopacki C. Pantev, Muenster Department of Neurobiology, University of lodz, Rewolucji 1905 No 66,90-222 Lbdz, Poland. The generation of EEG theta rhythm in the mammalian limbic cortex is a prime example of rhythmic activity that involves central mechanisms of oscillations and synchrony. In 1986 we demonstrated for the first time that bath perfusion of hippocampal slices with the cholinergic agonists resulted in theta-like oscillations. The coincidence in properties of the on vivo and in vitro recorded Not received rhythmic slow activity leads to a general conclusion that the generation of theta in both these preparations share common mechanisms. However, one more issue should be addressed. The known ability of CCH induced epileptiform activity (when administered in an appropriate concentration) would suggest that theta-like activity also has an epileptiform component. The theoretical implication of this suggestion would be that theta-like activity reflects the physilogical and pharmacological properties of epileptiform discharges. The experiments we have been conducting for the last 10 years on slice preparations suggest that the in vitro induced theta-like activity does not reflect the physiological and pharmacological properties of epileptiform activity. Since it was much more in common with the naturally occuring theta then with epilepsy, we have adapted the term "theta-like" activity. 38 Tuesday, Symposium: Cortical sources . Transient and Steady State Responses of Somatosensory and Neuromagnetic Sensorimotor Rhythms L4uditoryCortex in Humans Alfons Schnitzler L.E Roberts" D. Bosnyak", W. Gaetz" D. cheyneh, C. Pantev'. Department of Neurology, Heinrich-Heine University, Dusseldorf, C ahm mi as^, and H weinbergh Departments of Tsychology Germany and dNuclear Medicine, hlcMaster University, Hamilton, Canada, rain Behaviour Laboratory, Simon Fraser University, The human cerebral cortex generates a variety of rhythmic Vancouver, Canada; 'Institute of Experimental Audiology, oscillations detectable directly from the cortex or the scalp. The University of Muenster, Germany. recent development of whole scalp neuromagnetometers has made non-invasive studies of oscillatory brain activity feasible in awake "Transient responses" are responses evoked by stimuli human subjects In this presentation, results of studies will be presented at long interstimulus intervals such that the brain surveyed which investigated the human magnetic mu rhythm returns to its initial state before the next stimulus occurs. If the originating close to the primary somatosensory hand area and stimulus is presented at shorter intervals so that responses to consisting of dominant frequency components near I0 Hz and 20 successive stimuli overlap in time, the procedure is referred to Hz. Sources of tlie 20 Hz component cluster anterior to those of the as a "steady state procedure" and the response as a "steady state 10 Hz component suggesting a dominant contribution of the response" (Regan, 1989). We have adopted steady state precentral motor cortex 10 Hz and 20 Hz rhythms exhibit a procedures for imaging sensory representations in experiments characteristic modulation after electric median nerve stimulation, on cortical plasticity in humans, because these procedures afford with a suppression immediately after the stimuli and a strong rapid acquisition of data and concentrate signal energy at known rebound above the prestimulus level within 500 Ins aftenvards This repetition rates. Present findings suggest that sensory rebound is left-hemisphere dominant and differentially affected by representations or "maps" derived from steady state procedures various motor tasks and passwe tactile stimulation of the hands Interestingly, the 20 Hz component is also modified when the differ from maps based on transient methods. The relation of subject imagines the performance of a motor task, such as steady state and transient responses is discussed. exploratory finger movements,
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